Helium mass spectrometer leak detection is a well-known leak detection technique. Helium is used as a tracer gas, which passes through the smallest of leaks in a sealed test piece. The helium is then drawn into a leak detection instrument and is measured. The quantity of helium corresponds to the leak rate. An important component of the instrument is a mass spectrometer, which detects and measures the helium. The input gas is ionized and mass analyzed by the spectrometer in order to separate the helium component, which then measured. In one approach, the interior of a test piece is coupled to the test port of the leak detector. Helium is sprayed onto the exterior of the test piece, is drawn inside through a leak and is measured by the leak detector.
Industries frequently require very low leak rates due to environmental regulations, desire for improved product yield, extension of technology into new fields, or various other reasons. The ion current in a helium mass spectrometer for very low leak rates is on the order of femtoamps. With prior art leak detector spectrometers, this exceedingly small signal is difficult to detect with sufficient stability to provide an unambiguous leak rate signal in a leak detector. The signal-to-noise ratio and the signal stability over time are therefore critical for high-sensitivity leak detection.
A mass spectrometer separates gas species by mass-to-charge ratio so the gases can be analyzed at a detector. By far, the most common tracer gas used in the leak detection industry is helium, which appears at mass 4 on the mass scale (helium of mass 4 with charge 1). For many years, an unknown source of background variation has hindered precise measurement of small helium leak detection signals.
Accordingly, there is a need for improved mass spectrometers and methods for trace gas leak detection.